1. Field of the Invention
This invention relates in general to electronic devices and, more particularly, to improved means and methods for providing leads to semiconductor or other electronic chips. As used herein the words device or devices are intended to refer to all kinds of electronic devices and integrated circuits which use connection means and leads of the sort described herein, including but not limited to semiconductor based devices.
2. BACKGROUND ART
In the electronics art, particularly the semiconductor device and circuit art, it is commonplace to provide light weight leads to devices that primarily function for signal processing and heavy leads to devices that carry substantial current. Wire bonding of thin wires and tab bonding of metal foils are examples of techniques commonly used for signal processing devices. Such wires or foils generally carry only microamperes or milliamperes, are typically a fraction of a mil to a few mils thick, and are generally welded directly to the bonding pads on the device.
With higher current devices, such as power diodes and transistors or integrated circuits where currents of amperes to tens or hundreds of amperes are required, the leads bonded to the device must be more robust. It is commonplace to use metal leads that are of the order of ten to hundreds of mils thick. They are frequently attached by soldering to the bonding areas on the device.
When such robust leads are required, it becomes increasingly difficult to align the leads with the bonding pads on the die or other electronic device and to maintain such alignment during the bonding process. If the leads and bonding pads on the die are misaligned, then manufacturing yield and reliability are reduced.
Accordingly, it is an object of the present invention to provide an improved means and method for fabricating power devices wherein at least one of the leads is self-aligning with respect to a lead frame and the bonding pad on the die to which the lead is to be attached.
It is a further object of the present invention to provide an improved means and method for fabricating power devices wherein the die is mounted on a leadframe and a connection to a bonding pad on the device is provided by a self-aligning contact clip which bridges between the die and another part of the leadframe.
It is an additional object of the present invention to provide an improved means and method for fabricating power devices wherein the leadframe and the self-aligning contact clip have mating surfaces for aligning the clip with respect to the leadframe during assembly.
It is a further object of the present invention to provide an improved means and method for fabricating power devices wherein the self-aligning contact clip partially floats temporarily during assembly on electrical coupling materials for connecting it to the die and to the leadframe.
It is a further object of the present invention to provide an improved means and method for fabricating power devices wherein the die also floats during assembly and self-aligns with respect to the contact clip and the die mount portion of the leadframe.
It is an additional object of the present invention to provide an improved means and method for fabricating power devices wherein self-alignment is automatic.
As used herein the words solder or solders are intended to include any electrically conductive attachment material which is semi-solid or at least partially liquid at some time during the lead attachment process. Non-limiting examples are conventional metal or metal alloys or metal loaded epoxies or other conductive plastics and the like.
As used herein, the words chip or die are intended to refer to electronic elements such as but not limited to diodes, transistors, thyristors, integrated circuits, resistors, capacitors and the like having at least one bonding region or pad thereon.